Clean Dual-Waste Fuel Combustion of Glycerol-Methanol Blend with Simulated Landfill Gas by Utilizing a Novel Fuel-Flexible Injector

This study investigates the co-combustion characteristics of dual-waste fuel composition i.e., liquid and gaseous waste fuel, glycerol/methanol (G/M) blend with varying amounts of simulated landfill gas (LFG), to mitigate the carbon footprint and greenhouse gas effect using a novel fuel-flexible injector. Glycerol, the largest oxygenated byproduct of biodiesel production, with moderate energy density makes clean and efficient combustion very challenging due to its high viscosity. Extracting pure glycerol from crude glycerol, which contains a significant amount of methanol, is expensive. A recently developed Swirl Burst (SB) injector employs a two-phase atomization mechanism, generating fine sprays immediately even for highly viscous G/M blends without preheating, rather than a typical jet core/film by a conventional air-blast atomizer. Thus, the SB atomization has achieved ultra-clean combustion for G/M 60/40 ratios by heat release rate (HRR), effectively representing crude glycerol. On the other hand, LFG is a natural byproduct of the decomposition of organic material in landfills, with major component of methane, rendering it as a biofuel candidate. Hence, this study explores the co-combustion performance of G/M 60/40 with simulated LFG (50/50 ratio of CH4/CO2 by volume) in a 7-kW lab-scale swirl-stabilized gas turbine combustor. The effect of varying simulated LFG HRR (0-7 KW) on combustion characteristics of G/M 60/40 flame by using an SB injector is investigated at a constant atomizing air to liquid mass ratio (ALR) of 2.5, constant total HRR of 7 kW, and an equivalence ratio (ER) of 0.75. The global flame characteristics investigated include the visual flame images, concentrations of carbon monoxide (CO) and nitrogen oxide (NOx), and temperature of the combustion gas product and the combustor outer wall. Results show that lean premixed and complete combustion is achieved for the dual-waste fuel (a high viscosity G/M blend with simulated LFG) without pre-heating fuel nor insulation due to the ultra-fine SB atomization and its high viscosity tolerance. The optimal combustion condition for minimal pollutant emission occurs (~ 2 ppm CO and ~0 ppm NOx) when the liquid and gaseous fuel components provide equal heat release rates, i.e., about 3.5 kW each. With the increase of simulated LFG, the presence of CO₂ dilutes the mixture, reducing the reaction rates and the flame temperature slightly. The clean and efficient co-combustion of dual waste fuel - G/M with simulated LFG, highlights the potential for simultaneously or independently utilizing liquid and gaseous waste fuels enabled by the fuel-flexible injector.